1. Field of the Invention
The present invention relates to variable displacement wobble plate type compressors for use in an automotive air conditioning system or the like and more particularly to such compressors of a type whose controllability under high speed operation is improved.
2. Description of the Prior Art
In order to clarify the task of the present invention, one conventional compressor of the above-mentioned type will be described with reference to FIG. 2, which is disclosed in Japanese Utility Model First Provisional Publications Nos. 64-56,577 and 1-160,179.
The compressor 3 shown in FIG. 2 is of a type in which the volume of compression chambers defined by a cylinder block 25 is varied in accordance with a suction pressure of a refrigerant returned to the compressor 3 thereby to control the refrigerant discharge from the compressor 3. With this, the inlet pressure of the compressor 3 is kept constant during its operation.
When, in an air conditioning system, the inlet pressure of the compressor is kept constant, the pressure of refrigerant at an outlet port of the evaporator is kept constant, so that undesired freezing of the evaporator under low load can be avoided. Furthermore, the compressor discharges refrigerant in accordance with thermal load applied to the evaporator, so that the number of ON-OFF switching of a magnet clutch can be correspondingly reduced. The reduction of such switching reduces or lightens undesired change in temperature of air blown into a passenger room as well as change in torque of the engine.
As shown in FIG. 2, the compressor 3 comprises a drive shaft 11 which is driven by an engine (not shown) through a belt (not shown), a pulley 2 and a magnet clutch 2a. A drive rod 11a is connected to the drive shaft 11 in a manner to extend normally thereto, so that the drive rod 11a is turned in a crank chamber 12 together with the drive shaft 11. A drive plate 13 is pivotally connected to the drive rod 11a through a pin 11b and arranged so that its angle of inclination with respect to the drive shaft 11 is variable. Thus, the torque of the drive shaft 11 is transmitted to the drive plate 13 through the drive rod 11a and the pin 11b.
A nonrotatable wobble plate 16 is slidably mounted on the drive plate 13 by way of a thrust bearing 14 and a radial bearing 15. The wobble plate 16 is provieed with a shoe 19 which is slidably connected to a guide pin 18 fixed to the casing 17 of the crank chamber 12. This arrangement prevents the wobble plate 16 from rotating within the crank chamber 12 while allowing the inclination thereof to be varied.
A plurality of equally spaced piston rods 22 are connected to the wobble plate 16. Pistons 23 are connected to the other ends of the piston rods 22.
When the drive plate 13 is rotated, the wobble plate 16 is moved in a manner to induce each of the pistons 23 to undergo reciprocative movement in the cylinders or bores 26 formed in the cylinder block 25. Thus, during the reciprocative movement of the pistons 23, each working chamber defined before the piston 23 is subjected to alternate volume change effecting pumping action. As shown, the chamber defined behind each piston 23 is communicated with the crank chamber 12.
A cylinder head 30 is formed with a suction chamber 29 and a discharge chamber 13. The suction chamber 29 is arranged to communicate with a conduit through which refrigerant is returned from an evaporator (not shown). Inlet valves 34 are operatively mounted on a valve plate 20, so that they control inlet ports 27 formed in the valve plate 20. Discharge valves (no numerals) are also mounted on the valve plate 20 to control outlet ports 28 which communicate the cylinders 26 (more specifically, working chambers) and the discharge chamber 33. The valve plate 20 is sandwiched between the cylinder head 30 and the cylinder block 25, and formed of three layers. The center layer is suitably recessed or apertured to form a communication passage structure therein as well become apparent hereinafter.
The refrigerant led into the suction chamber 29 is also supplied through a connecting passage 32a to an intake pressure chamber 32 formed in the cylinder head 30, and then the refrigerant is supplied to a bellows chamber 64 through a first connecting passage R1.
The refrigerant compressed in the cylinders 26 is discharged into the discharge chamber 33 through the controllable outlet ports 28 and then discharged through a pipe (not shown) to a condenser (not shown). Part of the refrigerant in the discharge chamber 33 is supplied to a discharge pressure chamber 35 formed in a valve chamber V.
The valve chamber V is formed in the cylinder head 30 between the intake and discharge pressure chambers 32 and 35. Within the valve chamber V, there is installed a valve case h for a control valve Cv. The control valve Cv is arranged to operate in accordance with the pressure of the refrigerant returned to the suction chamber 29. That is, when the pressure of the returning refrigerant is relatively low, the control valve Cv closes a first valve port 40 and opens a second valve port 47, and while when the pressure of the returning refrigerant is relatively high, the control valve Cv opens the first valve port 40 and closes the second valve port 47. The control valve Cv has at a lower portion thereof a first valve element 36 and at an upper portion thereof a second valve element 39. The first valve element 36 controls the first valve port 40 with an aid of a bellows 37 which expands and contracts in a manner to establish an equilibrium between the pressure prevailing in the intake pressure chamber 32 and a spring 38 disposed in the bellows 37.
The first valve element 36 is formed with an operation rod 46 whose leading end is formed with the second valve element 39, so that movements of the first and second valve elements 36 and 39 are synchronously carried out. The first and second valve elements 36 and 39 are so arranged that as the first valve element 36 is moved toward a closed position, the second valve element 39 is moved toward an open one and vice versa.
With this arrangement, when the thermal load on the evaporator is low, the refrigerant which is returned to the compressor 3 has not absorbed much heat and thus produces a relatively low pressure in the suction chamber 29. Under this condition, the pressure (which will be referred to as "intake pressure Ps" hereinafter) in the intake pressure chamber 32 is low, and thus the bellows 37 expands and moves the first and second valve elements 36 and 39 upward as seen in the drawing. With this movement, the second valve port 47 is largely opened and part of the refrigerant (which will be referred to as "discharge pressure Pd") which is compressed by the piston 23 under compression stroke and discharged through the corresponding control outlet port 28 is supplied to the crank chamber 12 through the second valve port 47 and a second connecting passage R2 which includes a passage 62, a passage 63, a passage 48, a center opening 44 and a center passage 45. Thus, under such condition, the pressure (which will be referred to as "crank chamber pressure Pc" hereinafter) in the crank chamber 12 is increased.
The angle of inclination of the wobble plate 16 is controlled by the pressure prevailing in the crank chamber 12, more specifically, by pressures applied to the pistons 23 in forward and rearward directions. When the pressure Pc in the crank chamber 12 increases and exceeds that prevailing in the suction chamber 29, the pressure differential acting across the pistons 23 induces a moment of force which rotates the wobble plate 16 and the drive plate 13 about the pin 11b in a direction to reduce the angle of inclination.
Under this condition, the stroke of the pistons 23 is reduced and the amount of refrigerant discharged by the compressor 3 is correspondingly reduced. That is, the amount of the refrigerant circulated in the cooling system becomes suitable to the lower thermal load on the evaporator. With reduction of the refrigerant, the intake pressure Ps of the compressor 3 is gradually increased and an essentially constant pressure Ps is resultingly maintained.
The compressed refrigerant supplied to the crank chamber 12 contains a trace of lubricant oil which is applied through the center passage 45 of the drive shaft 11 and its drain port 45b to the radial bearing 15 which is arranged between the drive plate 13 and a sliding surface 15a of the wobble plate 16.
When the thermal load on the evaporator is high, the intake pressure Ps increases. This induces the bellows 37 to contract and move the first and second valve elements 36 and 39 downward as seen in the drawing. With this movement, the first valve port 40 is opened and the second valve port 47 is closed. Accordingly, the highly compressed discharge pressure Pd is not supplied to the crank chamber 12. However, when the intake pressure Ps is smaller than the pressure Pc in the crank chamber 12, the refrigerant in the crank chamber 12 is supplied to the suction chamber 29 through a third connecting passage R3 which includes a cylinder passage 61, a passage 41, the first valve port 40 and the bellows chamber 64. With this, the crank chamber pressure Pc becomes equal to the intake pressure Ps.
Thus, due to the work of the above-mentioned moment of force, the wobble plate 16 and the drive plate 13 are maximally inclined relative to the drive shaft 11 thereby increasing the stroke of the pistons 23. Thus, the amount of refrigerant discharged by the compressor 3 is correspondingly increased and thus becomes suitable to the higher thermal load on the evaporator. With increase of the refrigerant, the intake pressure Ps of the compressor 3 is gradually reduced and an essentially constant pressure Ps is resultingly maintained.
However, the above-described conventional compressor 3 has encountered drawbacks due to its inherent arrangement in which the surrounding of the bellows 37 serves as not only a pressure sensing means but also a refrigerant flowing means. That is, when, like in the case of the higher thermal load on the evaporator, the refrigerant from the crank chamber 12 is forced to flow through the third connecting passage R3, the dynamic pressure of the refrigerant is applied to the bellows 37. Under this condition, there is produced a pressure differential between the real intake pressure Ps and the pressure Ps' actually sensed by the bellows 37. In fact, the relationship of "Ps'&gt;Ps" is established. Thus, due to the work of the moment of force applied to the wobble plate 16 and the drive plate 13, the angle of inclination of them relative to the drive shaft 11 is subjected to an undesirable change by a degree corresponding to the pressure differential. In fact, in such case, the angle of inclination of the wobble plate 16 and the drive plate 13 is further increased and thus the stroke of the pistons 23 is further increased resulting in that the intake pressure Ps of the compressor 3 is further reduced.
When the compressor 3 runs at high speed, it is necessary to increase the pressure Pc in the crank chamber 12 and reduce the stroke of the pistons 23. However, in this case, the amount of the refrigerant flowing around the bellows 37 is correspondingly increased and the above-mentioned pressure differential is further increased. Thus, the controllability of the compressor 3 is lowered.